An automotive headlight with a high-pressure gas discharge lamp is described in German Patent Application No. 35 19 611 A1. In the described headlight, a molded housing is provided on the rear part of the reflector. The housing contains an electronic ballast that supplies the lamp with a high frequency starting and operating voltage. The high-pressure gas discharge lamp is inserted directly into the ballast through an opening in the reflector. An elastic sealing compound is inserted between the reflector and the molded housing to protect against harmful effects of moisture and corrosion. The ballast is supplied with voltage from the vehicle""s on-board electric system over a simple pair of cables.
In the described automotive headlight with a high-pressure gas discharge lamp, the molded housing is described explicitly as made of plastic. Together with the installation site directly on the reflector, this serves to design and arrange the ballast in the motor vehicle so that it is protected from the effects of weather without requiring any additional space; electric sparkover to other parts of the vehicle being prevented and the high-voltage lines being short to reduce capacitive losses.
This plastic housing for the ballast is not capable of dissipating enough of the heat generated in its interior by the lamp and its electronic unit. In addition, this plastic housing is unable to prevent interference voltage generated in its interior by the electronic unit of the ballast from being radiated out of the housing. Electronic components and devices in the engine compartment are thus endangered by the interference voltage emitted. Therefore, the required electromagnetic compatibility of this arrangement is not guaranteed.
An object of the present invention is to provide an automotive headlight with a high pressure gas discharge lamp having guaranteed dissipation of heat to protect the electronic unit accommodated in the interior of the housing, plus total shielding of the interior of the housing from the environment so that ballast-generated interference voltage is not radiated out of the housing. The electromagnetic compatibility of the automotive headlight with a high-pressure gas discharge lamp designed according to the present invention is thus ensured. This is an extremely important prerequisite for practical use. The parts contained in the interior of the housing are protected and shielded from effects from the external environment, while increasing their functional reliability.
According to the present invention, the housing is designed to dissipate heat and provide electromagnetic shielding to dissipate the heat generated by the electronic unit and possibly also the high-pressure gas discharge lamp and to provide a shield against the resulting electromagnetic radiation.
According to one embodiment of the present invention, the housing is provided with an internal and/or external coating to provide a shield against electromagnetic radiation from the electronic unit or the environment.
In an alternative embodiment, the material provided for the housing may be one that not only dissipates heat but also fulfills the function of providing electromagnetic shielding.
For more reliable and more intense dissipation of heat, the housing of the present invention is provided with parts that enlarge the surface area, in particular in the form of cooling ribs, for the purpose of dissipation of heat.
According to the present invention, the high pressure gas discharge lamp maybe either permanently or replaceably attached to the housing.
To make handling of installation simple and acceptable, the housing may be attached to the reflector by means of a standardized locking mechanism, in particular a bayonet lock.